Featured Research

from universities, journals, and other organizations

Study Shows Humans Have Ability To Track Odors, Much Like Bloodhounds

Date:

August 30, 2005

Source:

University of California - Berkeley

Summary:

Neuroscientists imaging the brain have confirmed a 40-year-old claim that humans have an untapped ability to localize odors in the same way we localize sounds. In fact, the brain seems to use the same brain region used by the ears to translate input from the two nostrils into spatial information. Someday, humans may vie with dogs and pigs in the ability to track smells.

Related Articles

Student volunteers presented with odors to one nostrilor the other could reliably discern where the odor was coming from, andfunctional magnetic resonance images of their brains showed that thebrain is set up to pay attention to the difference between what theleft and right nostrils sense, much the way it can localize sounds bycontrasting input from the ears.

"It has been very controversialwhether humans can do egocentric localization, that is, keep their headmotionless and say where the spatial source of an odor is," said studycoauthor Noam Sobel, associate professor of psychology at UC Berkeleyand a member of the campus's Helen Wills Neuroscience Institute. "Itseems that we have this ability and that, with practice, you couldbecome really good at it."

In future experiments, UC Berkeleybiophysics graduate student Jess Porter and Sobel plan to trainvolunteers to track odors in the field and test the limits of odorlocalization in humans.

Porter, Sobel and their colleagues reported the results in the August 18 issue of the journal Neuron.

Ina review appearing in the same issue of the journal, Jay A. Gottfriedof the Department of Neurology at Northwestern University's FeinbergSchool of Medicine noted that the UC Berkeley findings open numerousavenues for further research. "Finally, what are the implications forthe Provençal truffle hunt?" he wrote, only partly tongue-in-cheek. "Inthe traditional world of the truffle forests, the dog (or pig) is king.The evidence presented here suggests that humans are every bit as wellequipped to carry out the search."

Forty years ago, Nobel Prizelaureate Georg von Békésy claimed that humans had the ability tolocalize odors, based on experiments in 1964 with human subjects. Hesuggested this was done the same way we locate sounds: by contrastingeither the intensity of the odor or the time of arrival.

Sincethen, however, scientists have had difficulty replicating hisexperiments, according to Sobel. One explanation for this failure wasthat von Békésy used chemicals that stimulate not only the olfactorynerve in the nose, but also a nasal sensory nerve, the trigeminalnerve. Most odors stimulate both, and some, like onions and ammonia,are stinging enough to bring tears to the eyes. Perhaps, somesuggested, von Békésy's subjects were localizing odors based ontrigeminal nerve stimulation, not olfactory nerve stimulation.

Toeliminate this confusion, Porter and Sobel used two odors with minimaltrigeminal stimulation - essence of rose (phenyl ethyl alcohol) andcloves (eugenol) - as well as two trigeminal odorants - propionic acid,which smells like vinegar, and amyl acetate, which smells like banana.They delivered the odors through a specially designed mask with anartificial septum that provided separate air flow to each nostril.

Inaddition, they conducted similar experiments on five volunteers who hadno olfactory nerves and therefore couldn't smell at all, a conditionknown as anosmia.

Normal subjects, 16 in all, were able to tellwhich nostril was receiving a squirt of scent, but anosmic volunteerscould only localize the trigeminal odorants, Sobel said. This showsthat humans are able to localize odors through the olfactory nervesalone.

"One possible objection is that the experimental set-up,with a mask that provides separate air flow to each nostril, isartificial. How behaviorally relevant is that?" said Porter. Subsequentexperiments not yet reported, however, provide additional support fortheir hypothesis that the ability to localize odors to one nostril orthe other is realistic.

The experiments were conducted with thesubjects' heads inside a functional MRI to allow the scientists to seewhich areas of the brain were most active during sniffing and attemptsto identify and localize odors. They found that the left and rightnostrils have separate areas of the primary olfactory cortex - thebrain's smell center - devoted to them, indicating that the brain atleast encodes information that could help it localize an odor. Asuccessful detection of an odor is accompanied by more activity in theregion of the olfactory cortex associated with the particular nostril.

"Whilea subject was doing this task, I could look at the brain and tell youhow accurate he or she would be on every trial and on the taskoverall," Sobel said. "So the fact that we have this predictive valuein the data really suggests that we have actually successfully capturedthe mechanism."

What's more, another area of the brain outsidethe olfactory cortex was very active during successful localization.This area, the superior temporal gyrus, is also involved in thelocalization of sounds and visual objects, Sobel said.

"It'sactually a very nice and elegant convergence of this area, the superiortemporal gyrus, that appears to transform non-spatial information intospatial information," he said. "Together, these results are the firstdescription of the mammalian brain mechanisms for extracting spatialinformation from smell."

One key difference between theirexperiment and previous experiments to replicate the results of vonBékésy is that Porter and Sobel asked their subjects to actively sniff,whereas many previous experiments prevented subjects from sniffing.

"Wethink that most people failed to replicate his results for that reason,that is, the extent to which they enabled natural behavior,specifically sniffing," Sobel said. "In some studies subjects asked tolocalize an odor wouldn't be allowed to sniff. That's almost likestudying auditory localization but having your ears plugged. Weactually enabled natural behavior, we enabled subjects to sniff, and wethink that's a major difference."

In addition to Porter andSobel, other authors of the Neuron paper were UC Berkeley seniorscientist Rehan M. Khan of the Department of Psychology and graduatestudents Tarini Anand and Brad Johnson of the Department ofBioengineering. The work was supported by grants from the NationalInstitutes of Health.

University of California - Berkeley. "Study Shows Humans Have Ability To Track Odors, Much Like Bloodhounds." ScienceDaily. ScienceDaily, 30 August 2005. <www.sciencedaily.com/releases/2005/08/050830070723.htm>.

University of California - Berkeley. (2005, August 30). Study Shows Humans Have Ability To Track Odors, Much Like Bloodhounds. ScienceDaily. Retrieved March 3, 2015 from www.sciencedaily.com/releases/2005/08/050830070723.htm

University of California - Berkeley. "Study Shows Humans Have Ability To Track Odors, Much Like Bloodhounds." ScienceDaily. www.sciencedaily.com/releases/2005/08/050830070723.htm (accessed March 3, 2015).

More From ScienceDaily

More Mind & Brain News

Featured Research

Mar. 3, 2015 — The literary great Marcel Proust wore ear-stoppers because he was unable to filter out irrelevant noise -- and lined his bedroom with cork to attenuate sound. Now new research suggests why the ... full story

Mar. 3, 2015 — Attendance at schools exposed to high levels of traffic-related air pollution is linked to slower cognitive development among 7- to 10-year-old children in Barcelona, according to a new ... full story

Mar. 3, 2015 — No significant change in home habits of smokers have been observed in the aftermath of a ban on smoking in public spaces, researchers report. Greater inspiration to kick the habit likely comes from ... full story

Mar. 3, 2015 — Heart function has been associated with the development of dementia and Alzheimer's disease through a new study. Participants with decreased heart function, measured by cardiac index, were two to ... full story

Mar. 3, 2015 — Children of recently separated or divorced families are likelier to drink sugar-sweetened beverages than children in families where the parents are married, putting them at higher risk for obesity ... full story

Mar. 3, 2015 — Although sedatives are often administered before surgery, a randomized trial finds that among patients undergoing elective surgery under general anesthesia, receiving the sedative lorazepam before ... full story

Mar. 3, 2015 — Why do people shake hands? A new study suggests one of the reasons for this ancient custom may be to check out each other's odors. Even if we are not consciously aware of this, handshaking may ... full story

Mar. 3, 2015 — It appears that stress markers in unemployed people can be found, independent of smoking, alcohol consumption and overweight/obesity. Results from a study suggest that long-term unemployment may be ... full story

Mar. 3, 2015 — On the heels of an American nationwide measles outbreak comes a report that campaigns aimed at scaring people about the consequences of non-vaccination might not be as effective as many think. ... full story

Mar. 3, 2015 — Doctors write millions of prescriptions a year for drugs to calm the behavior of people with Alzheimer’s disease and other types of dementia. But non-drug approaches actually work better, and carry ... full story

Related Stories

Dec. 1, 2014 — The receptors activated by two odors have been identified by researchers using a new method that tracks responses to smells in live mice. Using a fluorescent protein to mark nerve cells activated by ... full story

Dec. 3, 2013 — New research challenges the two dominant theories of how people localize sounds, explains why neuronal responses to sounds are so diverse and shows how sound can be localized, even with the absence ... full story

May 30, 2012 — Humans can identify the age of other humans based on differences in body odor. Much of this ability is based on the capacity to identify odors of elderly individuals, and contrary to popular ... full story

Oct. 24, 2011 — Instinctive mothering behavior towards care of newborns has long been recognized as a phenomenon in humans and animals, but now research has shown that motherhood is associated with the acquisition ... full story

Oct. 17, 2010 — Neurobiologists have created mice that can "smell" light, providing a potent new tool that could help researchers better understand the neural basis of olfaction. The work has implications ... full story

ScienceDaily features breaking news and videos about the latest discoveries in health, technology, the environment, and more -- from major news services and leading universities, scientific journals, and research organizations.